Effective Electro-Optical Modulation with High Extinction
Ratio by a Graphene–Silicon Microring Resonator

Graphene opens up for novel optoelectronic
applications thanks to its high carrier mobility, ultralarge absorption
bandwidth, and extremely fast material response. In particular, the
opportunity to control optoelectronic properties through tuning of
the Fermi level enables electro-optical modulation, optical–optical
switching, and other optoelectronics applications. However, achieving
a high modulation depth remains a challenge because of the modest
graphene-light interaction in the graphene–silicon devices,
typically, utilizing only a monolayer or few layers of graphene. Here,
we comprehensively study the interaction between graphene and a microring
resonator, and its influence on the optical modulation depth. We demonstrate
graphene–silicon microring devices showing a high modulation
depth of 12.5 dB with a relatively low bias voltage of 8.8 V. On–off
electro-optical switching with an extinction ratio of 3.8 dB is successfully
demonstrated by applying a square-waveform with a 4 V peak-to-peak
voltage.